The smallpox vaccines ordered by the UK and the US are likely to be equally
effective -- or, possibly, they may be equally ineffective.

Reports that the strain of smallpox vaccine now being stockpiled by the UK
will not work, while the US stockpiled vaccine will, are wrong, according to
smallpox experts.

But New Scientist can also reveal that neither is certain to work. This is
because the old tried-and-tested vaccines, which eradicated smallpox, were
made on the skin of live animals and the new ones will not be.

The US currently has a stockpile of 165 million doses of the old-style
smallpox vaccine. But because of fears following the events of September 11
that terrorists may possess smallpox, the US decided to order an extra 55
million doses of new vaccine a year from the UK-based firm Acambis.

In April 2001, the UK followed suit by ordering an undisclosed number of
doses of new vaccine from the British firm PowderJect, to add to its three
million dose stockpile of old vaccine.

Weaponised strain

The UK contract had already been criticised by opponents of the UK's
governing Labour Party, because PowderJect CEO Paul Drayson has donated
money to Labour. But on Tuesday, allegations surfaced in the UK press that
the choice was not even medically warranted, as the UK vaccine will be
derived from the Lister strain, while the US will use a strain named after
the New York City Board of Health.

The charge is that Lister will not protect against an especially virulent
strain of smallpox, India-1967, which was weaponised by the tonne under the
old Soviet bioweapons programme. It is feared that this strain is most
likely to have fallen into unfriendly hands.

The NYCBH strain probably does work against India-1967, as a Soviet
derivative of it was widely used during the smallpox eradication campaign in
India.

"But Lister vaccines were used very widely in India, and they worked" says
Ian Simpson of the World Health Organization. In fact, Lister was the most
widely used smallpox vaccine in the world, according to the WHO, which
supplied the strain to vaccine manufacturers. The WHO advised either strain
could be used in the eradication programme.

Scraping skin

But all that may have little to do with the vaccines being made now. The old
vaccines were made by infecting animals with the Vaccinia virus, a
smallpox-relative, and then scraping infected material off pustules on their
skin.

That is no longer an acceptable production method, because of the
possibility of contamination with other pathogens. Both Acambis and
PowerJect will be making their vaccines under sterile conditions in large
cultures of cells.

However, the European Agency for the Evaluation of Medicinal Products
(EMEA), the EU's governing body for pharmaceuticals, warns in a June report:
"There is little or no experience of the effectiveness of cell culture grown
vaccines against smallpox."

It notes that production using tissue cultures would select for strains of
the virus that thrive in those cells, meaning that the final strain emerging
from intensive cell culture may bear little comparison to its parents.

Safety tests

The EMEA warns that the effect of this on the efficacy and safety of the
vaccine needs to be studied. The effect might be so large compared to
differences in the parent strains that the EMEA felt it could not recommend
either Lister or NYCBH as the parent strain of choice.

Simpson cautions that "there is no reason to think tissue-culture produced
vaccines will necessarily be less effective than the old vaccines". It is
simply not known.

Safety studies are underway for the Acambis vaccine, but there is no way to
test either vaccine's effectiveness at protecting humans -- smallpox has
been eradicated. EMEA recommends tests in animals using related pox
diseases, and measuring antibodies after vaccinating humans, but it is not
known what antibody profile means safety.